1. Field of the Invention
The present invention relates to a crawler vehicle such as a crawler crane and a hydraulic excavator. Particularly, the present invention relates to a device for positioning crawler frames movably provided on the both left and right sides of a track frame.
2. Description of Related Art
A description will be given to a structure of the crawler vehicle such as the crawler crane below. A lower travelling body onto which an upper rotating body is mounted includes a track frame and a pair of left and right crawler frames. In outer peripheries of the crawler frames, crawlers are installed. In such a crawler frame structure, a distance between centers of the crawlers is expanded in order to improve stability while the crane is working. The distance between centers of the crawlers is contracted while the crane is carried by a trailer. The above is influenced by legislation.
As the related art of such a crawler vehicle, a description will be given to a crawler vehicle disclosed in Japanese Utility Model Publication No. Hei7-15828. In the crawler vehicle, crawler frames are provided with through holes passing through in the width direction. To the through holes, axles of a track frame are slidably fitted. Between the track frame and the crawler frames, hydraulic cylinders are provided. The hydraulic cylinders move the crawler frames in the width direction along the axles of the track frame.
Japanese Utility Model Publication No. Hei7-15828 also discloses a positioning device for, when the crawler frames are moved to an expansion position or a contraction position along the axles of the track frame, positioning and fixing the crawler frames at the above positions. The positioning device is provided with a connection link arranged in the width direction along a side surface of the axle of the track frame, a bracket for fixing one end of the connection link to the crawler frames, and a link connection member fixedly attached to the side surface of the axle of the track frame for supporting the other end side of the connection link. By connecting the connection link to the link connection member with a connection pin at the expansion position and the contraction position, the positioning device fixes the crawler frames to the track frame at both the positions.
In the conventional crawler vehicle, from a view of ensuring the stability at the time of crane operation and the width at the time of conveyance, distance between centers of crawlers is only switched to maximum and minimum. Therefore, at a working place such as a mountain area where a grounding space of the crawlers is limited, there is a need for performing a land leveling preparation so as to maximize the distance between the centers of the crawlers before conveying a working vehicle there. When the above preparation cannot be performed, the crane operation has to be performed with the minimum distance between the centers of the crawlers.
However, when the land leveling preparation is performed, the start of crane operation of the crawler vehicle is delayed. Further, with a crawler vehicle incapable of performing the land leveling operation by itself such as the crawler crane, there is a need for introducing other working vehicle for land leveling separately from the crawler vehicle. Thereby, working cost is increased. When the work is performed with the minimum distance between the centers of the crawlers, it is not possible to exhibit a sufficient performance of the crawler vehicle.